Listening at sunset from atop the ancient Mayan temples poking out of the jungle, today one hears the cacophony of howler monkeys, squawking macaws, and toucans. Bat falcons dive toward the verdant roof of Spanish cedar, mahogany, and ceiba trees stretching as far as the eye can see - an emerald canopy gently dissolving into a smoke-blue mist.

The Maya Biosphere Reserve is part of North America's largest surviving rain forest, and accounts for a large portion of the 10 million "protected" acres sprawling across three nations. A botanist's paradise. A logger's dream. A refuge for endangered species and narco-traffickers. The last frontier for cattlemen and migrant farmers.

In the last 20 years, the population of the Peten has soared from 20,000 to about 300,000. The region has been opened up by petroleum and logging companies, by the Guatemalan Army in search of leftist guerrillas, and, yes, by archaeologists exploring the Mayan ruins. Settlers have followed in their paths.

"We've got 250 to 300 people arriving daily. We can't cope with the flood," says Rafael Franco Corso, mayor of San Benito. "The Peten is disappearing at a frightening rate."

As civilization penetrates, this wilderness slides toward the same fate as the Mayan empire. Since the mid-1980s, conservation groups in Mexico, Guatemala, and Belize have managed to have some chunks of forest set aside as reserves, multiple-use areas, and buffer zones.

But so far these are little more than reserves on paper. Illiterate campesinos arriving to clear a few acres for corn and beans know nothing about "biosphere reserves." Often, the cattleman, loggers, and chicleros (who tap trees for chewing gum base) have lived here for generations and see environmental proclamations as outside threats to be skirted by whatever means possible. Local government is weak or non-existent. "This is the Wild West," says one official here.

So environmentalists face the daunting task of helping control the region's development or at least channel humanity's march into the area.

What is being contemplated is a bold attempt to develop cross-border alliances between academics, conservationists, and public officials. Mexicans, Guatemalans, and Belizeans are starting to work together and treat the region as a single entity.

"Flukes of history have divided this forest into three political entities. A satellite photo of this region shows one forest, one ecosystem. This is the moment to coordinate across the boundaries to keep this ecosystem alive," says James Nations, Latin America vice president for Conservation International, a Washington-based environmental group.

The moment may be right because the three governments have seldom been on better terms. Last September Guatemala agreed to restore diplomatic relations with Belize. Guatemala has long claimed the former British colony was founded on its territory, and severed ties in 1981. Meanwhile, Mexico is hosting the Guatemalan peace talks and working to return some 45,000 war refugees to Guatemala.

This progress takes place against a backdrop of evident presidential concern for the environment. For example, Mexican President Carlos Salinas de Gortari announced in late March the indefinite suspension of plans for a controversial dam project on the Usumacinta River, which runs along the Mexico-Guatemala border.

AT a conference in Flores, Guatemala, in early April, sponsored by the MacArthur Foundation, a Chicago-based philanthropic organization, conservationists, scientists, and academic groups working in the region met to discuss common challenges and how they might form a conservation cooperation zone.

The structure and funding of such a zone were left unclear, but participants seemed to agree that the Guatemala-based Central American Commission for Environment and Development and the Switzerland-based International Union for Conservation of Nature (IUCN) might spearhead its development.

"We need to share information and solutions," says Juan Carlos Godoy, IUCN's Central American representative. "How, for example, do you confront illegal activities given the lack of roads, lack of communications, and the absence of state officials and police?"

Flying low over the rain forest the day before the conference, an illegal logging camp is spotted. The pilot makes a note of the location. But an expert on the flight who requests anonymity says there is a good chance the wood will be shipped unimpeded to mills in Mexico.

"Of course, the military sees everything that moves in and out of the forest. But the loggers have false documents. And the military is either paid off or takes the attitude that its job is to fight the communists, not be conservation police." The military's role was discussed privately among participants but not raised at conference sessions.

One suggestion from the conference was that the few existing park rangers and police from the three countries meet to swap information on firefighting and the illegal trade in hardwoods, wildlife, and archaeological artifacts.

COOPERATION is seen as crucial to what conservationists say is one of the best opportunities in the world to save a major wilderness. "If we can't do it here, we won't be able to do it anywhere," says Alfred Nakatsuma, a United States Agency for International Development official working in the region.

Mr. Nations concurs: "This is a test case for conservation and sustainable development in the world."

Indeed, conservationists are increasingly becoming developers.

"We're not a rich country. We don't have the luxury of preserving something just to look at it," says Marco Venicio Solares, president of the Peten Wood Industry Association. "Conservation programs are fine but the only way to stop the destruction is to send money directly to the campesinos migrating here. Unless they have something to eat, nothing will change."

Saving a forest, then, is largely a question of community-by-community development solutions. Migrants arriving at the reserve must perceive the forest as more valuable standing than cut and burned for farmland or pasture. Conservationists are only beginning to explore how to make such "sustainable development" work.

Eco-tourism and photo safaris are among the more obvious approaches. But there are other experiments underway. For example, with international funding, the conservation group Program for Belize recently bought 202,000 acres of land to create the Rio Bravo Conservation and Management Area along the Guatemala border. To halt the advance of nearby villages into the forest, private investors are raising money to build a chicle processing plant. This will create jobs and is aimed at raising community awarenes s of the forest as a resource to be utilized with care.

Near the Montes Azules Biosphere Reserve in the Mexican state of Chiapas, Conservation International has a pilot project to make pictures for sale, using the different colored wings of butterfly species that are not endangered.

Bioncenosis, a private group working near the Calakmul Reserve in Campeche, has a program to take sport hunters into the woods and charge for every animal shot. For example, taking a wild turkey will cost $200.

"We must create tropical forest development options just outside the reserve, so there's a buffer zone around it," notes Martin Goebel, executive director of Conservation International in Mexico.

But Guatemala-based environmentalist Santiago Billy opines that these new industries alone "won't stop people from arriving and deforesting. You need labor-intensive work." Perhaps, he says, that means maquiladora industries or assembly plants. He predicts that the solutions will be too slow in coming. "We could lose 40 percent of the reserve in the next decade or two. Conservation is a romantic concept but it won't work if there aren't jobs."

Another challenge is gaining community acceptance of conservation-oriented solutions.

"The decision to make an area a biosphere reserve is seldom a democratic one taken by vote of the people in the area," says Brian Houseal, regional director of The Nature Conservancy. "But it must become democratic in practice for it to work."

Ismael Ponciano of Guatemala's Mario Dary Foundation for Conservation of the Environment and Natural Resources recounts the case of Punta Amatique. This fishing village was declared part of a protected area. Three years ago, conservationists contracted with two members of the community to help with their work. But the chosen surrogates were not respected within the community and their efforts were resisted.

The conservationists then hired an anthropologist with the instructions: "Go live in the community and look for shared points of interest." The anthropologist slowly gained the community's trust. There had been no weddings or baptisms in the isolated town for five years because there was no priest. The anthropologist was asked for help. He replied, "I don't have any expertise in this area. But if you fix up the church and give me a boat and gas, I'll try and fetch a priest." And he did.

After a year of such help, in March the community elected representatives to manage and defend the local environment.

"We can't arrive with our concepts of conservation and force them on people. It takes time to see how our interests coincide. It's a two-way street of learning," Mr. Ponciano says.

A similar attitudinal shift may be starting to occur in the Peten.

"Four years ago, if you said you were an environmentalist, the people here thought you were either crazy or a communist. That's changing. Even the military is at least giving lip service to the concepts," says Mr. Nakatsuma. "Biosphere reserves, sustainable development, [and] buffer zones don't mean a thing if you don't have a change in mental attitude on the ground."